How to select (or Traverse to) iFrame parent of a document...

I have an iFrame on a page where I am calling .mouseup(function()) on it's document child. Once in the mouseup function, I need to refer to a specific sibling of the iFrame. Unfortunately, I cannot figure out how to traverse backwards to the iFrame element from $(this) - where $(this) is the document. I get a null set returned when I try $(this).parents().

Any thoughts?